﻿using System.Linq.Expressions;
using Artemis.Core.Modules;

namespace Artemis.Core;

internal static class ExpressionUtilities
{
    internal static Expression CreateDataModelAccessor(DataModel dataModel, string path, string parameterName, out ParameterExpression parameter)
    {
        parameter = Expression.Parameter(typeof(object), parameterName + "DataModel");

        // Create an expression that checks every part of the path for null
        // In the same iteration, create the accessor
        Expression source = Expression.Convert(parameter, dataModel.GetType());
        return CreateNullCheckedAccessor(source, path);
    }

    internal static Expression CreateNullCheckedAccessor(Expression source, string path)
    {
        // Create an expression that checks every part of the path for null
        // In the same iteration, create the accessor
        Expression? condition = null;
        foreach (string memberName in path.Split('.'))
        {
            BinaryExpression notNull = Expression.NotEqual(source, Expression.Constant(null));
            condition = condition != null ? Expression.AndAlso(condition, notNull) : notNull;
            source = Expression.PropertyOrField(source, memberName);
        }

        if (condition == null)
            throw new ArtemisCoreException($"Failed to create a null-check for path {path}");

        // Combine the null check and the accessor in a conditional statement that returns the default for the type if null
        return Expression.Condition(condition, source, Expression.Default(source.Type));
    }
}